This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This is an open-label, multiple-dose, ascending dose study in approximately 85 subjects in 3 age groups (ages greater than 2 to less than 6 years, 6 to less than 12 years and 12 to 16 years), to be conducted at approximately nine investigative sites with access to general clinical research centers (GCRCs) with pediatric experience. Each of these sites will enroll approximately 12 subjects (total of approximately 108 subjects) to allow for discontinuation of subjects prior to study completion and titration of a sufficient number of subjects to each dose level. Baclofen will decrease in the activity of the muscles that are over active making it easier for the subject to move and better interact with his/her surroundings and other people Primary objectives: 1. Determine pharmacokinetic parameters of oral baclofen in children with spasticity associated with CP. 2. Describe the relationship between plasma concentrations of oral baclofen and clinical measures of spasticity. 3. Determine optimal dosing range and interval for administration of oral baclofen for use in a randomized clinical study of safety and efficacy. Secondary objectives: 1. Describe the relationship between plasma concentrations of oral baclofen and measures of strength, function, ease of care, pain/comfort and health related quality of life. 2. Describe the safety and tolerability of oral baclofen in children with spasticity associated with CP. 3. Investigate preliminarily whether oral baclofen improves dystonia.